Generally, a piston pump is used in a brake fluid pressure control apparatus for a vehicle. For example, JP-2006-504029-A discloses a piston pump in which a piston is formed of a needle (a first piston portion) and a resin portion (a second piston portion), and a passage for sucking a working fluid therethrough is formed in the contact surface between the first and second piston portions. The working fluid passage extends in the radial direction of the piston.
Also, JP-2005-090402-A discloses a piston pump which is composed of a metal-made piston and a resin-made sheet member and includes multiple communication grooves respectively formed in the outer periphery of the piston to extend in the axial direction. A working fluid is allowed to flow from a suction passage through the communication grooves into a pump chamber.
According to the piston pump of JP-2006-504029-A, since the working fluid passage extends perpendicularly to the piston moving direction, the reciprocating operation of the piston does not contribute to the suction of the working fluid. Therefore, the suction of the working fluid merely rely on the negative pressure of a working chamber, resulting in the poor suction efficiency.
Also, according to the piston pump of JP-2005-090402-A, since the metal-made piston has a complicated structure (multiple communication grooves), the piston needs a complicated working operation, resulting in the increased costs of the composing parts of the piston pump.
On the other hand, JP-2008-111355-A discloses a piston pump in which a cylinder is formed by cutting a metal-made member to thereby enhance the durability. Also, JP-H11-257245-A discloses a piston pump in which a cylinder is formed of a resin molding to thereby enhance the workability.
In the piston pump of JP-2008-111355-A, since the cylinder is formed by cutting the metal-made member, production of such cylinder requires much time and labor as well as the cost thereof. In view of this, the material that can be cut efficiently may be selected as the material for forming the cylinder. However, when such easily-cuttable material is used, a heat treatment will be required to enhance the durability of the cylinder after the cutting working, and the further cutting working may be required to remove the distortion caused by the heat treatment. Since such working operation is necessitated, the cost can not be reduced.
In the piston pump of JP-H11-257245-A, since the cylinder is formed of a resin molding, a cutting working is not necessary. However, in this case, the cylinder does not have durability that can withstand the repeated sliding movements of the piston. When specific material such as carbon fiber is used to enhance the durability of the cylinder, the cost of the cylinder and thus the cost of the piston pump will be increased.